U.S. Pat. No. 3,001,096 issued to Fredrick A. Mosby, on Sep. 19, 1961 for a Terminal Structure for Double-Ended Lamps shows the general structure of the double ended lamps being manufactured by the applicant.
Normally, as disclosed in the Mosby patent, double ended lamps are assembled by positioning a filament in an envelope, with the lead ends of the filament being held in clamps. The envelope ends are then flame heated and sealed to the sealing foils. The lamp is filled with the proper gases, and tubed off. The lamp is then roughly a glass tube with two lead wires protruding from opposite ends. Contact buttons are then attached to the leads. A ceramic insulator is then cemented in place between the glass or quartz end of the lamp, and around the contact button. The cement fills the region between the contact button and the glass or quartz end of the lamp.
The contact buttons commonly are either crimped or welded to the exposed outer leads of the lamp. Unfortunately, these methods are not always fully successful, and durable. The lead wire to contact button connection may fail, causing internal arcing in the lamp seal region. The arcing breaks down the connection further, causing overheating, or electrical failure. The contact button may also separate from the lamp. Also, the crimp or weld may not be square with the filament, and seal. The button contact is then either realigned, that is bent into position, or cemented in place at an incorrect angle. The misaligned contact buttons do not sit in the contact supports properly, so the lamp, and therefore the filament is misaligned with respect to the lamp housing optics.
Crimping only mechanical bonds the lead and the contact button. The mechanical bond may deteriorate in a long life lamp. For example, the contact button can become loose during repeated thermal cycling of the lamp, causing an intermittent contact. The intermittent contact leads to arcing and destruction of the contact and base assembly. Crimping is used on lamps with current ratings of less than eight amperes or where the contact and lead temperature is expected to be less than about 350 degrees Celius.
For lamps with higher current ratings, or higher expected operating temperatures, the button contacts are welded to the exposed lead ends. Welded button contacts require an extra manufacturing step of cleaning the lead first to achieve an adequate weld. The major problem with welded button contacts, is that the lead may become embrittled by the welding. Weld current may not be applied through the filament, so the weld must be made by contacting the exposed lead end between the quartz and the contact button. This is necessarily a small contact region. The second weld contact is made with the exterior side of the contact button, and does not present a problem. The weld heat causes the lead to recrystalize and be brittle. An embrittled lead is easily fractured, leading the same internal arcing, and arc induced break down as in a crimped contact button.
Both of the old methods of crimping and welding are subject to errors in lead cleaning, trimming, and crimper or welder set-up. There is also a loss of time and material in having to trim the lead after lamp sealing. Applicant has found a different method of manufacture that substantially resolves these problems.